1. Field of the Invention
The present invention relates generally to systems for controlling gear selection in compound transmissions and, particularly, to systems for accomplishing gear selection on auxiliary transmissions.
2. Description of the Prior Art
Transmissions providing a plurality of selectable gear ratios between input and output are in common use in transportation. Compound change gear transmissions of the type having one or more auxillary sections connected in series with the main transmission section are also in common use in transportation. One example of a compound change gear transmission in one having a single combined range/splitter type auxiliary section. Examples of such transmissions may be seen in U.S. Pat. Nos. 3,283,613 and 3,648,546.
The main section of such transmissions are shifted by manually selectable gear shift mechanisms. An Operator accomplishes gear selection by shifting a gear shift lever. Auxiliary sections of such transmissions are typically shifted by two independent air cylinders; a range cylinder and a splitter cylinder. The range cylinder is used to position the transmission in LOW or HIGH range. The splitter cylinder is used to position the splitter in ON or OFF position. The splitter cylinder and the range cylinder must be interlocked to coordinate respective gear positioning to assure proper operation. That is; when the range cylinder is in HIGH position, the splitter cylinder may be shifted into either On or OFF position. When the range cylinder is in low position, the splitter must be OFF or shifted to OFF position.
The range cylinder transmissions known in the art are controlled by selectively applying pressure to the LOW or alternatively to the HIGH side of the range cylinder. Thus, when HIGH range has been selected, the HIGH side of the range cylinder will be filled with pressurized air and the LOW side vented to atmosphere. When LOW range has been selected, the reverse occurs.
The splitter cylinder of transmissions known in the art are controlled by continuously applying pressure to a first side and selectively pressurizing or depressurizing the opposing side. The differential in the piston area causes the piston to assume an initial position when both sides are equally pressurized. When one side is depressurized, the pressure on the opposing side acts to displace the piston to the opposite splitter position. An interlock is accomplished, preventing splitter On when in LOW range, by using the pressure from the HI side of the range cylinder to convey the splitter ON command, That is, if the range cylinder is in LOW position, no pressure will be available to communicate the depressurization command to shift the splitter to ON condition. Whereas, if the range cylinder is in HIGH position, pressure will be available to convey the depressurization command to shift the splitter to ON condition.
Thus, the auxiliary section is controlled by two separate air switches which are typically mounted on the transmission main section gear shift lever. One switch receives pressurized air from the system reservoir and selectively delivers pressurized air to a slave valve associated with the range cylinder. The second switch receives pressurized air from the HIGH side of the range cylinder and selectively delivers air to the slave valve associated with the splitter cylinder. To accomplish this objective, four air lines must traverse the wall of the vehicle cab.
It would be appreciated as an improvement if the two supply lines could be combined as one, reducing the total to three while maintaining the interlocking function.